This invention relates to a floatation module and method of using the floatation module. More particularly, but not by way of limitation, this invention relates to a floatation module and method for safely reducing the rig hoisting requirements to run tubular strings into sub-sea wells and well bores.
As the energy industry continues to search the globe for hydrocarbon reservoirs, the search has increasingly focused in the world's oceans. Economical hydrocarbon reservoirs are increasingly being discovered and developed in deep water tracts located in remote and exotic places on the planet. Floating drilling platforms, such as mobile offshore drilling units (MODU's), are anchored in water depths of more than 9,200 feet and are dynamically positioned in water depths greater than 10,000 feet.
In combination with this deep water drilling, the actual wells drilled are in increasingly deeper water in order to penetrate commercially feasible hydrocarbon reservoirs. Hence, these wells can exceed 34,000 feet in depth. The equipment required to safely drill ultra deep water wells is large, extremely heavy, and difficult to safely handle. As understood by those of ordinary skill in the art, the lifting and lowering capacity of the drilling rigs, including MODU's, are loaded to the maximum safe working loads.
For instance, if an operator is running a casing string into a well bore to a sub-sea wellhead, the operator is required to lift out of the casing slips then lower that proper amount of casing. However, the operator will also be required to pick-up and lower a landing string in combination with the casing, and wherein the ultimate length of the landing string will be basically equal to the distance between the rotary table and sub-sea well head at the sea floor. Therefore, the combined weight of the casing string and the landing string could push the safe hoisting and drill pipe slip's capacity of the MODU to its maximum designed safe working loads.
The landing string is specifically designed to provide the very high tensile strengths (now rated to 1,500,000 lbs. working load) to safely land out casing in the sub-sea well head. As the water depth increases, the length and weights of the landing string increase proportionateley. Existing MODU's are now operating at or near their maximum hoisting capabilities with loads of 1,500,000 to 2,000,000 pounds. Casing loads of 1,500,000 pounds translate to dynamic loads of 1,750,000 lbs or more (depending on hole condition, fluid characteristics, casing designs, friction) when picking up out of the slips. In some cases, this exposes the entire load path/hoisting system (top drive, subs, crown sheaves, derrick, slips and brakes) to maximum loading.
Numerous problems involving drill pipe slip crushing and catastrophic slip failures have occurred which have required new heavier designs that even now barely meet load requirements. Loading the hoisting system to the maximum of its design creates several safety concerns including, but not limited to: special landing strings being designed that are heavier wall, which further exacerbates the load handling requirements; rig hoisting system capability to safely handle extreme loads (static/dynamic); the rig's capability to safely apply over-pull in tight hole conditions; the requirement of inspection of hoisting and braking system prior to the job; and dynamic loads which reach and/or exceed safe working capabilities.
A prior art technique, known as floating, is sometimes used to reduce casing loads during running. The floating technique entails running the casing without completely filling the entire length with fluid, therefore establishing buoyancy due to the air inside. This presents several concerns for operations, equipment, and the health and safety of the rig crew. For instance, some of the problems encountered include: extremely high differential pressures on float equipment; failure of float equipment could cause immediate overloading of rig hoisting system caused by loss of buoyancy, which would be catastrophic; well control and/or stuck pipe due to swabbing or suction if floats fail; casing collapse; and, removal of air in casing effects circulation and cementation of the casing.
Therefore, there is a need for an apparatus and method for running and landing casing from floating drilling platforms. There is also a need for a device and method that can reduce the rig hoisting requirements to safely run casing strings from floating drilling platforms. These as well as many other needs will be met by the invention herein disclosed.